Field of the Invention
The present invention relates to a coating nozzle to be attached to the paint-discharge leading-end section of a coating apparatus for blowing a high-viscosity paint onto an object to be coated.
Description of the Related Art
Coating nozzles for blowing high-viscosity paints, such as acrylic-resin-based paints, polyester-resin-based paints, polyurethane-resin-based paints, epoxy-resin-based paints, or melamine-resin-based resins, onto objects to be coated have been known publicly. For example, in automobile manufacturing plants, high-viscosity paints have been blown onto automotive bodies in order to give them rust-preventive, waterproof and vibration-damping properties, with use of coating nozzles being installed on robots, as disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2012-11284 and Japanese Unexamined Patent Publication (KOKAI) Gazette No. 11-179243 (hereinafter, being referred to as “Related Art No. 1” and “Related Art No. 2,” respectively).
FIGS. 6 and 7 illustrate a coating nozzle that Related Art No. 1 discloses. FIG. 6 shows a plan-view diagram of a coating nozzle 110. FIG. 7 shows a front-view diagram of the coating nozzle 110 when being viewed on a side of the paint-discharge leading end. The coating nozzle 110 comprises an introduction passage 117, an internal space 116, and a nozzle slit 115. The introduction passage 117, the internal space 116 and the nozzle slit 115 are communicated with each other, and are disposed in this order from the bottom to the top in FIG. 6. A high-viscosity paint, which has been supplied to the internal space 116 through the introduction passage 117, is reserved temporarily in the internal space 116 whose space spreads more than that of the introduction passage 117, and thereby the inner pressure is uniformized. Then, the high-viscosity paint, which has been extruded out from the internal space 116 to a nozzle-slit inlet 115G, is discharged from a nozzle-slit outlet 115E to an object to be coated while spreading radially to the object. As a result, the high-viscosity paint is coated as a strip shape with a predetermined patterned width on a surface of the object to be coated.
The nozzle slit 115 is formed as a strip shape with an arc configuration going along an arc in the coating nozzle 110 that is formed as a substantially-sectored shape when being viewed in the planar diagram. The intervening space between a nozzle-slit outlet 115E and the nozzle-slit inlet 115G is designed to have a uniform interval substantially. As illustrated in FIG. 7, the nozzle-slit outlet 115E has an opening configuration (or discharge-mouth configuration) that takes on a rectangular shape whose slit opening is “x” and slit width is “y.” As illustrated in FIG. 6, the nozzle slit 115 converges linearly from the nozzle-slit outlet 115E to the nozzle-slit inlet 115G toward an imaginary apex “c” being held between the two equilateral sides of an imaginary isosceles triangle. Note that, in the imaginary isosceles triangle, the bottom side is made by an imaginary chord that connects linearly between an opposite end “e” of the nozzle-slit outlet 115E being formed as an arc shape and the other opposite end “f” thereof, and each of the bottom angles is made by an angle “α” (hereinafter, being referred to as a “slit angle ‘α’”). That is, the nozzle-slit 115 spreads linearly from the imaginary apex “c” with an opening angle “β” (i.e., “β”=180°−2×“α”).
When a distance between the imaginary apex “c” and the opposite end “e” (or the opposite end “f”) is labeled a first radius “a,” and another distance between the imaginary apex “c” and a central point “d” in the width-wise direction of the nozzle-slit outlet 115E is labeled a second radius “b,” the first radius “a” and the second radius “b” are designed to be equal to each other (i.e., the first radius “a”=the second radius “b”). Thus, the nozzle-slit outlet 115E is formed as a true arc shape about the imaginary apex “c” serving as the center. Moreover, the high-viscosity paint is spouted substantially perpendicularly to an opening face of the nozzle-slit outlet 115E that takes on a true arc shape.
FIG. 8 is a graph for illustrating relationships between the discharge rates and shear velocities in the conventional coating nozzles that Related Art Nos. 1 and 2 disclose. When the shear velocity is labeled “D” (s−1), the discharge rate is labeled “q” (c.c./minute), and the slit opening is labeled “x” (mm) that is shown in FIG. 7, and the slit opening area is labeled “s” (mm2), the shear velocity “D” can be found by such a calculating equation as follows:“D”=[{“q”/60}/“x”}/“s”]×1,000.Note that the slit opening area “s” can be found as a product “x”·“y” of the slit opening “x” and the slit width “y” because it is equivalent to the opening area of the nozzle-slit outlet 115E when being viewed in the planar diagram.
A line “L1” in FIG. 8 shows a relationship between the discharged rate “q” and the shear velocity “D” when the slit opening “x” was set at 0.4 mm (i.e., “x”=0.4 mm) and the slit width “y” was set at 39 mm in the conventional coating nozzle that Related Art No. 1 discloses. Moreover, a line “L2” in FIG. 8 shows a relationship between the discharged rate “q” and the shear velocity “D” when the slit opening “x” was set at 0.6 mm (i.e., “x”=0.6 mm) and the slit width “y” was set at 43 mm in the conventional coating nozzle that Related Art No. 2 discloses. In addition, a line “L3” in FIG. 8 shows a relationship between the discharged rate “q” and the shear velocity “D” when the slit opening “x” was set at 0.8 mm (i.e., “x”=0.8 mm) and the slit width “y” was set at 43 mm in the conventional coating nozzle that Related Art No. 2 discloses.
As one of the achievements of earnest studies by the present inventors, it was revealed that whether the coated appearance (e.g., flatness and/or smoothness) of a coated high-viscosity paint on an object to be coated is satisfactory or not is intimately related to the shear velocity “D” when the high-viscosity paint passes through the slit of a coating nozzle. Specifically, when the shear velocity “D” falls in a range of from 5,000 to 20,000 s−1 roughly, the high-viscosity paint is likely to produce a satisfactory appearance. When the shear velocity “D” falls outside the range, however, undulating phenomena occur where the resulting coated form of a high-viscosity paint “P” undulates greatly as shown in FIG. 9. As a result, such a case might possibly arise where the resultant film thickness cannot be constant or uniform in the coated high-viscosity paint “P,” because no flatness and/or smoothness can be secured in the coated high-viscosity paint “P.”
In automobile manufacturing plants, a coating nozzle, which has been installed to a robot, is used to discharge the high-velocity paint “P” at such a flow rate that makes the discharge rate “q” fall in a range of from 3,000 to 10,000 c.c./minute roughly. The hatched area in FIG. 8 shows an area where the shear velocity “D” becomes from 5,000 to 20,000 s−1 when the discharge rate “q” falls in a range of from 3,000 to 10,000 c.c./minute in a setting of the actual employment. Therefore, when the shear velocity “D” is contained within the hatched area in FIG. 8, like the ideal line “L0” in the drawing, in a range where the discharge rate “q” falls in a range of from 3,000 to 10,000 c.c./minute in a setting of the actual employment, it is effective to reduce the occurrence of faulty painted appearances when a coating nozzle is used actually.
As the lines “L1,” “L2,” and “L3” in FIG. 8 indicate, however, the related-art coating nozzles might possibly result in such cases that they yield the shear velocity “D” that falls outside the hatched area in a setting of the actual employment where the discharge rate “q” falls in a range of from 3,000 to 10,000 c.c./minute. Therefore, the related-art coating nozzles have not been designed so as to be capable of reducing the occurrence of faulty coated appearances in a setting of the actual employment. Hence, the related-art coating nozzles might possibly have been associated with the following fears: quality problems in which the coated high-viscosity paint “P” interferes with other component parts because the undulating phenomena have thickened the resulting film thickness depending on the discharge rate “q” of the high-viscosity paint “P”; and problems causing the increment of painting costs because the high-viscosity paint “P” has been coated in excessive amounts, which are more than those being directed in engineering drawings, to result in the occurrence of material wastes.
Moreover, in a case where the related-art coating nozzles are simply provided with a smaller slit opening “x” so as to enlarge the shear velocity “D” in order to reduce the occurrence of faulty coated appearances, they might possibly be associated with a fear of the occurrence of clogging in the nozzle slit when it might not be possible to fully inhibit foreign materials from remaining or residing within the high-viscosity paint “P.” In addition, in another case where the related-art coating nozzles are provided with the above-described slit angle “α” which has been made smaller so as to enlarge the diffusion of the high-viscosity paint “P” in the width-wise direction, in order to secure a predetermined patterned width, they might possibly be associated with another fear of the occurrence of cracked patterns as shown in FIG. 10.